Tissue expander

ABSTRACT

A soft tissue expander has enhanced performance through use of differential and directional expandability, continuous expansion capability, increased base and dimensional stability, increased soft tissue purchase by virtue of unique surface topography, and results in improved cavity contour after expansion. Expansion means may be provided to expand the implant in a desired direction. In the preferred embodiment, an expander or implant has an exterior surface defining a volume, the exterior surface including a base portion, a first wall and a second wall, wherein the second wall is relatively thinner than the first wall. A fill port, which may be integrally molded into the expander, is included. As the expander is inflated, differential expansion occurs with the relatively thin second wall section expanding more than that of the first wall section. The base may include ribs or other molded-in structures to increase structural integrity. Optionally, a bellows may be included on the exterior surface of the expander, the bellows optionally including a limiting ring. Molded-in geometric patterns may be employed to present textured internal, as well as external surfaces to the implant or expander. Compressive structures may be used on the inside or outside surface of the implant.

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application is a continuation of U.S. application Ser. No.08/823,119, filed on Mar. 25, 1997, which is a file wrapper continuationof U.S. application Ser. No. 08/472,781, filed on Jun. 7, 1995, nowabandoned, which is a continuation-in-part of application U.S. Ser. No.08/198,651, filed on Feb. 18, 1994, now U.S. Pat. No. 5,653,755, whichis a continuation of U.S. application Ser. No. 07/837,284, filed on Feb.18, 1992, now abandoned, which is a continuation of U.S. applicationSer. No. 07/137,871, filed on Dec. 22, 1987, now U.S. Pat. No.5,282,856, and is related to application Ser. No. 07/799,773, filed onNov. 27, 1991, now U.S. Pat. No. 5,383,929, which is a continuation ofU.S. application Ser. No. 07/325,444, filed on Mar. 20, 1989, nowabandoned, which is a divisional of U.S. application Ser. No.07/137,871, filed on Dec. 22, 1987, now U.S. Pat. No. 5,282,856, andfurther related to application Ser. No. 07/325,881, filed on Sep. 11,1990, now U.S. Pat. No. 4,955,907, which is a divisional of U.S.application Ser. No. 07/137,871, filed on Dec. 22, 1987, now U.S. Pat.No. 5,282,856. The priority of these prior applications is expresslyclaimed and their disclosure are hereby incorporated by reference intheir entirety.

FIELD OF THE INVENTION

[0002] This invention relates to implantable prosthetic devices. Moreparticularly, it relates to implantable tissue expanders for use inplastic and reconstructive surgery to stretch tissue in order to augmenta soft tissue deficit, cover an ablative defect, or reconstruct aportion of the body.

BACKGROUND OF THE INVENTION

[0003] Implantable prosthetic devices have been used in numerouslocations in the body. The most common use has been for restoring orimproving upon normal body contour or augmenting as well asreconstruction of the female breast. The most common breast prosthesisis similar to that disclosed in U.S. Pat. No. 3,293,663 to Cronin, inwhich there is a flexible elastomeric container, typically silicone,which is filled with a soft gel, typically silicone gel or a salinesolution or a combination of both.

[0004] A tissue expander is surgically implanted beneath tissue to bestretched and is filled at appropriate intervals with biocompatiblefluid. After sufficient stretch has been achieved the tissue expander isremoved and the newly available tissue used to cover a soft tissuedefect or used to create a replacement body part. A breast tissueexpander may be made convertible to a definitive, long-term,augmentative prosthesis, also known as an “implant”.

[0005] As the field has progressed from simple wound coverage toreconstructing more realistic body parts incorporating prostheticdevices, especially in the case of the female breast, it has becomeevident that more control of the expansion process would be desirable inorder to speed the process, to minimize the morbidity and the number ofsurgeries involved, as well as to refine the end result.

[0006] In breast reconstruction, major problems associated with thetissue expansion process include difficulty in creating a normalteardrop shaped and normally pendant breast due to the inability tocreate a properly shaped pocket. Presently the only options are eithermultiply chambered expanders with multiple injection ports or laminatedcomponent structures. These are commercially considered less thandesirable because they are prohibitively expensive. They arefunctionally suboptimal as slippage at the soft tissue/expanderinterface may occur and there is a lack of purchase at the interfacewhich is associated with inappropriate thinning and grossly non-uniformexpansion of tissue.

SUMMARY OF THE INVENTION

[0007] A soft tissue expander, which is a temporary implant into thebody, utilizes structures having differential and directional expansioncapability to project the expander or implant in the desired directions.In a preferred embodiment, an expander or implant has an exterior surface defining a volume, the exterior surface including a base portion, afirst wall and a second wall, wherein the second wall is relativelythinner than the first wall. A fill port, which may be integrally moldedinto the expander, is included. As the expander is inflated,differential expansion occurs with the relatively thin second wallsection expanding more than that of the first wall section.

[0008] The base may include ribs or other molded-in structures toincrease structural integrity. Additionally, the base may include “toes”or other structures which project out from the base, such as flanges,which are adapted to provide a broader base or footprint to theexpander. The expander enjoys increased base and dimensional stabilityas a consequence.

[0009] Additional directional expansion may be achieved through use ofoptional bellows molded into a portion of the expander shell wall. Asthe expander is inflated, the bellows provide a projection beyond thatprovided by the basic expander. Limiting rings may be used, such assurrounding the bellows at the bellow base which mates to the expander.

[0010] Molded-in geometric patterns may be employed to present varyingtextured surfaces to the internal or external surfaces of the implant orexpander. This results in increased soft tissue purchase by virtue ofunique surface topography and assists in obtaining differentialexpansion by virtue of the differential purchase resulting from thedifferent molded-in patterns. Textured surfaces also have the effect ofweakening periprosthetic scar tissue. Optionally, compressive structuresmay be beneficially used on the surface of the implant or in theinterior of the implant.

[0011] In another preferred embodiment, a tissue expander uses multiplechambers wherein the chambers are in fluid communication. Preferably,one of the chambers is adapted for placement behind a muscle, such asthe pectoralis muscle if the expander is used for breast reconstruction.

[0012] Accordingly, it is an object of this invention to provide animproved implant which functions as a soft tissue expander.

[0013] It is a further object of this invention to provide an enhancedability to weaken periprosthetic scar as well as to permit the surgeonto improve cavity contour at the end of the expansion phase.

[0014] It is yet a further object of this invention to create variableyet controlled purchase at the tissue/expander interface and to providefor differential expansion capability by varying wall thickness. It isanother object of this invention to provide for directionalexpandability of the expander.

[0015] It is an object of this invention to enable the surgeon to createa more natural soft tissue envelope for the human breast including amore natural inferior sulcus.

[0016] It is a further object of this invention to provide animplantable prosthesis which permits postimplantation accommodation oftotal volume, either more or less than the volume at implantation.

[0017] It is a further object of this invention to provide animplantable mammary prosthesis which permits post implantationaccommodation of implant projection which is defined as the distancefrom the chest wall pole of the implant to the opposite pole of theimplant.

BRIEF DESCRIPTION OF THE FIGURES

[0018]FIG. 1 is a cross-sectional view of a telescoping projectionelement of an implant or expander.

[0019]FIG. 2 is a cross-sectional view of an implant or expanderincluding a telescoping projection element, where the apical portion ofthe expansion element is an expansion chamber.

[0020]FIG. 3 is a cross-sectional view of an implant having variablewall thickness.

[0021]FIG. 4 is a cross-sectional view of FIG. 3 at line A-A.

[0022]FIG. 5 is a cross-sectional view of an expander including abellows expansion member.

[0023]FIG. 6 is a cross-section of a pressure accommodation element.

[0024]FIG. 7 is a cross-section of an expander having a base includingintegral ribs.

[0025]FIG. 8 is a cross-section of FIG. 7 at A-A.

[0026]FIG. 9 is a cross-sectional view of a multi-chambered expander.

[0027]FIG. 10 is a cross-sectional view of a textured covering for useon the implant or expander.

DETAILED DESCRIPTION OF THE INVENTION

[0028] The present invention is based upon the previously disclosedmethod of liquid silicone molding of textured implants (my U.S. Pat. No.5,354,338), directional expansion of implants and varying wall thickness(my U.S. Pat. No. 4, 955, 907), pressure adaptive structures, (my U.S.Pat. No. 5,383,929), as well as novel elements disclosed herein andmethods of manufacture of the combination of elements.

[0029] The term implant is used broadly to include any foreign objectwhich is inserted into the body. An expander is an object which is animplant because it is placed within the body. An expander is ordinarilyplaced within the body, and over time, such as a matter of weeks or afew months, is gradually inflated so as to expand and move adjacent softtissues. After expansion, the expander may be removed from the body andthe space filled with another implant, or optionally, the expander maybe converted into a permanent implant in the body. In the latter case,this may involve changing the fluid in the implant/expander, such asfrom saline to a gel or a: triglyceribe or other biocompatible fluid.Thus, the terms implant and expander are used interchangeably herein.

[0030]FIG. 1 shows a cross-section of a telescoping projection elementwhich may be configured as the mammary prosthesis 10 proper or may beconfigured as a projection element of a more complex implant orexpander. Toroid elements 12 may be solid or fluid-filled and serve torestrict horizontal displacement of the shell, yet pemit verticalexpansion.

[0031] The apical portion 14 of the expansion chamber 16 is made thin inorder to permit preferential dilation of this region. The apical portion14 is thin relative to other first wall portions 22. The fill port 18serves to permit input of expansion fluid, which causes the expander toincrease in volume, and to undergo differential expansion in therelatively thin wall, apical areas 14. A base region 20 is relativelythick and provides stability to the implant 10 when inserted in thebody. Optionally, sheet teflon (PTFEe) 24 may be used to cover thetoroidal regions 12.

[0032]FIG. 2 shows a cross-section of an implant 30 consisting of astack of either hollow or solid toroid elements 32 held in apposition bya projection element 34 that traverses the central opening 36 of eachtoroid element 32 and which by virtue of the enlarged top and bottomportions serves to maintain all elements of the implant in intimatecontact. The apical portion 38 of the projection element is an expansionchamber which may be filled through the bottom or top piece fluid port40. The surfaces of the toroid elements are protected by a covering ofPTFEe sheets 42 which are sewn or otherwise affixed to each other at thegreater periphery. The tube is shown covered by tubular PTFEe tominimize friction. The apical portion 38 is relatively thin walledcompared to first wall portions 44 or the based 46. Optionally, abiocompatible covering 48 may be added onto the implant 30.

[0033]FIGS. 3 and 4 show a cross-sectional and cut-away view at A-A of apreferred embodiment of a liquid silicon elastomer injection moldedtissue expander. This structure is superimposed upon the “male” positiveportion of the injection mold which produces the product. The “male”positive portion of the mold necessarily is supported by support column50, shown in phantom.

[0034] The tissue expander 52 has continuously variable or varying wallthicknesses, however, in the preferred embodiment shown, there is asingle, first thick region 54 of the implant incorporating substantiallythe smaller pole of the expander as well as extending to the “toe” 56region of the base 58 and in the opposite direction from the smallerpole toward, and incorporating, the region of the fill port 60. The thinregion 62 incorporates substantially the larger pole of the expander.

[0035] The “toe” region 56 is a molded flange-like extension of theintegrally molded base 58 portion of the expander and is more generallydescribed as an extension of any thickened portion of an expander. Thefunctions of the “toe” region include: as an anchoring mechanism for thethick region of the expander as collagen matrix collects in space 64which is defined as the recess between the “toe” (flange) 56 and theouter surface of the expander shell. Maturation of scar tissue resultsin increased tensile strength of the scar in space 64, which byshortening along the long circular axis of the scar, results in firmanchoring of the “toe,” (flange) to the immediately adjacent tissues ofthe body.

[0036] The textured surface topography of the base region as well as allother texturized surface portions of the expander help to cause firmadherence between the expander and enveloping scar, as well as todisorganize scar, and thus weaken it. The “toe” (flange) 56 regionassists greatly in maintaining dimensional as well as positionalrelationships. Upon surgical explantation of the tissue expander 52 thesurgeon often reshapes the interior of the cavity created by theexpander. The “toe” region, having formed a firm scar band in the regionof the space 64, allows the surgeon the flexibility of convenientlycreating more laxity of the wall of the cavity created by the expanderby simply excising the scar band to the extent desired. By not excisingthe scar band thus formed the surgeon can limit the further stretchingof the involved region of the cavity. It will be appreciated that thevolume of scar and, therefore, the total tension in that scar is adirect function of the size/volume of space 64. The “toe” region 56 thushelps greatly in configuration angulation of the cavity margin.

[0037] Variably rounded peripheries of the base of a cavity can beengineered by varying base 58 thickness, expander wall 54 and 62thickness, “toe,” (flange) 56 thickness and length, differentialexpansion capability, degree of purchase at the tissue/expanderinterface, and volume/pressure relationships generated within theexpander.

[0038] The injection fill port 60 of the expander is directly molded-inand thus incorporated into the molded shell structure of the tissueexpander. In FIGS. 3 and 4, the fill port 60 is incorporated as athickened cup-like region 66 of the molded integral tissue expandershell. This structure is fully disclosed in an application filedsimultaneously with the present application, entitled “Injection Portfor Implantable Tissue Expander.” The position of the fill port 60relative to any other structural element of the tissue expander ishighly variable. In this embodiment, the void in the base created by thesupport column is patched with a separately molded silicone elastomerpatch.

[0039]FIG. 4 shows the cross-sectional detail of FIG. 3 at line A-A. Byway of example, for an expander useful for mammary reconstruction, thefirst wall 54 would be relatively thick, such as from 0.020 to 0.100inches, and may have a thickness of approximately 0.030 inches. Thesecond wall 62 would be relatively thinner, such as from 0.005 to 0.050inches and would, for example, have a thickness of 0.020 inches. Thebase portion 58 may be of a different thickness, preferable relativelythick compared to the first wall 54 and second wall 62, and could be,for example, 0.050 inches thick.

[0040]FIG. 5 shows the “bellows” 70 structure as incorporated within thethin region 62 in this preferred embodiment but may be incorporated inany region of an expander where differential and directionalexpandability is required. Under internal pressure the limiting ring 72,which may be a separately molded silicone elastomer or another suitablematerial, restricts the expansion of the lesser diameter of the“bellows” 70 resulting in directional expansion of the bellows along anaxis perpendicular to the plane of the limiting ring and away from thecenter of the expander lumen. The degree of directionality of expansionof the bellows is greater than is otherwise possible.

[0041]FIG. 6 is a cross-sectional view of a compressive structure 70which may optionally be inserted into a chamber, such as at 66 on FIG.5. The pressure accommodation element may be affixed to the outer and/orinner surfaces of the shell or may be permitted to float freely withinthe saline or gel matrix within FIG. 6 is included to clarify the textpertaining to the comprehensive description of the invention. It must beclarified here that this structure is molded separately and adhesivelysecured to the internal surface of the expander not at the time ofmolding the expander shell, but rather at a later manufacturing step. Ashell 72 preferably includes an evaginated insert 74 which contains gasor fluid. Optionally, openings 76 in the shell 72 permit flow to theinsert 74.

[0042] The Pressure Adaptive Structure may be adhesively attached to theinterior of the base of this embodiment. With reference to my U.S. Pat.No. 5,383,929, FIGS. 18, 22-24, the pressure adaptive structureillustrated in FIG. 6 is only one of many configurations of gas-filledstructures well suited to serve the function of a “continuous” expandingstructure within the tissue expander. For example, a curled sealedtubular gas-impervious structure, or a toroidal structure with the samecharacteristics would likewise suit the requirements for this structure:the ability to contain a biocompatible gas within the structure, whichunder the increased pressure exerted by the fluid during periodicaugmentative filling causes the expander to partially collapse and in sodoing compresses the gas substantially. The consequent increasedpressure generated within the lumen of the pressure adaptive structurecontinues to exert outward pressure on the fluid in the lumen of theexpander proper. At all times, the pressure inside the pressure adaptivestructure and the pressure inside the lumen of the tissue expanderproper are in equilibrium, however the gas-filled pressure adaptivestructure exercises the necessary recoil needed to continue theexpansion of the entire tissue expander in order to overcome theresistance offered by the tissues undergoing expansion.

[0043]FIG. 7 is a cross-section of an expander 80 having a baseincluding integral ribs. FIG. 8 is a cross-section of FIG. 7 at A-A. Inthis structure, reinforcing ribs 82, 84 are integrally formed in thebase 58 of the implant/expander 80. This provides relative rigidity tothe structure. Optionally, the ribs may be formed in any direction, orin any pattern or configuration to achieve the desired rigidity. Ashown, longitudinal ribs 82 run into the plane of FIG. 7 and traverseribs 84 run parallel to the plane of FIG. 7.

[0044]FIG. 9 is a cross-sectional view of a multi-chambered expander 90.While two chambers are shown in FIG. 9, more chambers 92 may be usedconsistent with the inventive concept. The first chamber comprises arelatively large chamber, and may incorporate a first relativelythick-walled portion 94, and a second relatively thin walled portion 96.The second chamber, or pumping chamber 98, is in fluid communicationwith the first chamber 92, such as at tube or passageway 100. For theapplication shown in FIG. 9, that is, expansion for breastreconstruction, the second chamber 98 is adapted for disposition betweenthe ribs 102 and the pectoralis muscle 104. A base portion 106 isintegral to the second chamber 98. Optionally, texturization 108 (shownpartially covering the implant) may be formed over the surface of theimplant, such as over the exterior disposed face of the implant, and onthe exterior portion of the base 108 directed towards the chest wall. Afill port 110 is provided. It will be appreciated that the pumpingfunction of the second chamber 98 in combination with pectoralis muscle104 could also be preformed by a mechanical pump integrated into thesystem.

[0045]FIG. 10 is a cross-sectional view of a textured covering for useon the implant or expander. The “nested hexcels” structural pattern 112may be attached to or part of the implant. The textured covering mayform the entirety or only a portion of the covering of the implant. Thehexcel with the largest perimeter 114 in this configuration is also thetallest and delimits hexagonal pools of biologic materials and tissuesat the interface between the implant and the body cavity. As scar tissueforms it is forced into concentric, nested rings of scar tissue which donot communicate freely and thus do not contribute to an integralcircumferential scar capsule.

[0046] The height of these nested hexcels structures may be varied.Also, the number, diameter or perimeter of the hexcel structures as wellas their wall thickness and shapes and characteristics may be varied. Itwill be further appreciated that a great number of geometric patternsmay be utilized for the purposes described here, including square andcircular patterns.

[0047] Various types of texturization are available. Using the preferredmanufacturing technique of this invention, namely injection molding, thesurface may easily be texturized with any desired form or pattern,whether predictable or random.

[0048] Method of Manufacture

[0049] The tissue expander is made of liquid silicone elastomer suppliedby NuSil Technology of Carpinteria, Calif., and is described in productliterature as Liquid Silicone Rubber MED-4840. The product is describedas a two-part system which is Platinum cured. The pre-mixed liquid partsA and B are injected into a preheated mold which is then heated furtherto 275-320 degrees Fahrenheit. Curing time ranges between 5-10 minutes.

[0050] The molded product is removed from the mold and furthervulcanized for 20-45 minutes in a separate oven at 275-375 degreesFahrenheit. Molded voids in the shell are then patched with a siliconeelastomer molded component. The tissue expander thus molded results in avariably textured and contoured shape with continuously variable wallthickness.

[0051] Optionally, the tissue expander may be molded with an integralchamber-like fill port incorporated directly into the whole structure atthe time of molding. A fill port may be molded separately and during alater stage of manufacture be made adherent to the shell-like expanderstructure either totally on the smooth internal surface of theshell-like structure or with a portion of the fill port projectingthrough the shell-like structure.

[0052] Illustrated in FIGS. 3 and 5 are two preferred embodiments of amolding tool positive with a product of the molding process superimposedon the tool. FIG. 3 illustrates the case where a single void in theshell-like structure results from the molding process as a result of thepresence of supporting column 50. This void is sized so as to accept aseparately molded fill port, which is adhesively attached to theshell-like expander. FIG. 5 illustrates the case where a fullyintegrated fill port or other appended structure is molded directly intothe expander proper.

[0053] In FIG. 3, a single resultant void is created at the region wheresupporting column 50 is attached to the positive portion of the moldingstructure. In FIG. 5, this void requires patching with a specialsilicone elastomer patch created specifically for this purpose. Inaddition to the positive portion of preferred-embodiment moldsillustrated in FIG. 3, there are two “female” portions of the mold whichserve to texturize the outer surface of the molded product. These femalemold elements slide up and down guide shafts to fully enclose thepositive mold element, or may slide in a plane substantiallyperpendicular to the axis of column. The variably dimensioned voidbetween the positive (male) and “female” portions of the mold serve todefine the variable wall thickness of the final molded siliconeelastomer product. Unique texturing of the mold as per U.S. Pat. No.5,354,338 is transferred to molded product in accordance withengineering specifications. Thin 62 and thick 54 regions of the wall ofthe balloon-like expander shell enable differential expansion, the thinregion enhancing expansion, the thick regions inhibiting it. Anadditional preferred embodiment feature permitting especiallyadvantageous directional expansion of a portion of a molded product isthe bellows-like structure 70 molded directly into the “larger pole”apex of the tissue expander. A further preferred embodiment of a tissueexpander is the inclusion of a gas-filled pressure adaptive structure(FIG. 6) within the lumen of the tissue expander as per my U.S. Pat. No.5,383,929. This structure is indicated in FIG. 6, “pressure adaptive”structure and is adhesively attached to the interior surface of thickregion.

[0054] The ability to extend the time intervals between periodicinjections of filler fluid, by virtue of continuous outward pressureexerted by an integral gas-filled pressure chamber, makes the processmore comfortable for the patient. Continuous expansion results inreaching final volume more quickly and is a clear advantage overexisting technology.

[0055] Though the invention has been described with respect to specificpreferred embodiments, many variations and modifications will becomeapparent to those skilled in the art. It is therefore the intention andexpectation that the appended claims be interpreted as broadly aspossible in view of the prior art in order to include all suchvariations and modifications.

What is claimed is:
 1. A covering for an implantable device comprising afirst surface, the first surface being non-textured, and a secondsurface having ridges and valleys.
 2. The covering of claim 1 furthercomprising PTFEe material.
 3. The covering of claim 1 wherein the ridgesand valleys of the second surface form nested geometric structures. 4.The covering of claim 3 wherein the nested geometric structures comprisenested hexcels.
 5. An implantable device covering comprising a sheet offlexible material having first and second surfaces, the first surfacebeing flat, the second surface having peaks and troughs and beingadapted to interface with body tissues.
 6. The covering of claim 5further comprising PTFEe material.
 7. The covering of claim 5 whereinthe peaks and troughs of the second surface form nested geometricstructures.
 8. The covering of claim 7 wherein the nested geometricstructures comprise nested hexcels.
 9. An implantable device andcovering comprising an implantable device, and a sheet of flexiblematerial attachable to the implantable device, the sheet including atissue interfacing surface, wherein the tissue interfacing surfaceincludes a plurality of structures forming ridges and valleys.
 10. Theimplantable device and covering of claim 9 wherein the covering furthercomprising PTFEe material.
 11. The implantable device and covering ofclaim 9 wherein the ridges and valleys of the tissue interfacing surfaceform nested geometric structures.
 12. The implantable device andcovering of claim 11 wherein the nested geometric structures comprisenested hexcels.
 13. An implantable device covering comprising a sheet offlexible material having first and second surfaces, the first surfacebeing non-textured, the second surface having first and second planarsurfaces, the first and second planar surfaces being in non-planarrelation.
 14. The covering of claim 13 further comprising PTFEematerial.